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Bug #79622 Imagewbmp outputs an white image with something incomprehensible.
Submitted: 2020-05-23 03:43 UTC Modified: 2020-05-23 09:29 UTC
From: cretu dot andrei at zoho dot com Assigned:
Status: Not a bug Package: *Graphics related
PHP Version: Irrelevant OS: Windows 7, X64
Private report: No CVE-ID: None
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 [2020-05-23 03:43 UTC] cretu dot andrei at zoho dot com 
Description:
------------
I'm using imagecreatefromjpeg to create an image from a source. Then I'm using imagewbmp to save it as .wbmp.

The image saved is 98% white with a small portion black.

Test script:
---------------
$image_object = imagecreatefromjpeg('http://i.pinimg.com/originals/5b/97/49/5b9749c4db7066138b085b28a229801f.jpg');

imagewbmp($image_object, 'new_image.wbmp');

Expected result:
----------------
A black and white image.

Actual result:
--------------
I see an image allmost white...

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 [2020-05-23 05:49 UTC] requinix@php.net
-Status: Open +Status: Not a bug
 [2020-05-23 05:49 UTC] requinix@php.net 
WBMPs only do black and white.
 [2020-05-23 06:12 UTC] cretu dot andrei at zoho dot com 
Have you tested the code ?

Here is the original image: https://ibb.co/WyRngKD
Here is the result: https://easyupload.io/9r4ka6

Is that ok ?
 [2020-05-23 06:21 UTC] requinix@php.net 
WBMPs. Are. Only. Black. And. White.

Most of your source image is light colored. It will be translated into white. The small portions that are dark will be translated into black.
 [2020-05-23 06:29 UTC] requinix@php.net 
If I load your source image into GIMP and have it convert the image to monochrome, which it does so in a smart way using dithering that GD cannot do, then save and convert with PHP, I get
https://easyupload.io/b86xdf
 [2020-05-23 09:29 UTC] cmb@php.net 
imagewbmp() only considers pixels with exactly $foreground color
to be foreground; all other color values are considered
background.  So just feeding in an arbitrary JPEG is not supposed
to work.  Instead, convert the JPEG to a palette image with only 2
colors, and then set $foreground to be either color no. 0 or 1.

<?php
$im = imagecreatefromjpeg(__DIR__ . '/79622.jpg');
imagetruecolortopalette($im, true, 2);
imagewbmp($im, __DIR__ . '/79622.wbmp', 0);
?>

The script above uses dithering with a result roughly similar to
what @requinix posted above.  Dithering is not strictly necessary,
though.
 
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